1. Field of the Invention
The present invention relates to a wiring substrate and an electronic parts packaging structure and, more particularly, a wiring substrate on which electronic parts are packaged by an ultrasonic flip-chip packaging and an electronic parts packaging structure in which the electronic parts are packaged on the wiring substrate.
2. Description of the Related Art
In the related art, a wide variety of packaging methods are proposed as the flip-chip packaging that is being quickly spread as the representative high-density packaging method. As one of the flip-chip packaging method, there is the ultrasonic flip-chip packaging method.
In the ultrasonic flip-chip packaging method, as shown in FIG. 1A, first an electronic parts 106 having bumps 108 thereon and a wiring substrate 100 having connection pads 104 on an insulating film 102 are prepared. Then, the bumps 108 on the electronic parts 106 picked up by the ultrasonic tool are arranged so as to oppose to upper surfaces of the connection pads 104 of the wiring substrate 100. Then, the bumps 108 on the electronic parts 106 are bonded to the connection pads 104 of the wiring substrate 100 by applying the ultrasonic vibration in parallel with the surface of the wiring substrate 100 in a state that the pressure is applied to the electronic parts 106.
Meanwhile, in many cases the resin is used as the insulating film 102 of the wiring substrate 100. As shown in FIG. 1B, since the insulating film 102 made of resin is relatively soft, sometimes the connection pads 104 are pushed into the underlying insulating film 102 by the pressure or the ultrasonic vibration applied when the ultrasonic flip-chip packaging is carried out, and are deformed. Therefore, since an energy of the ultrasonic vibration is not sufficiently transmitted as the energy to bond the bumps 108 on the electronic parts 106 and the connection pads 104 of the wiring substrate 100, such a problem exists that it becomes difficult to bond the bumps 108 and the connection pads 104 with good reliability.
Also, in the ultrasonic flip-chip packaging, the ultrasonic vibration has such a characteristic that its energy is ready to transfer to the center portion of the electronic parts 106 rather than both end portions. Therefore, the bonding characteristic of the bump 108 and the connection pad 104 is varied between the center portion and both end portions of the electronic parts 106, and thus reliability of the bonding is lowered in some cases.